Traditionally, jeans are constructed using a strong twill weave. Yarn is cut lengthwise and then dyed either blue or black. Then additional yarn is cut crosswise and dyed white. These yarns have what is called a "hard twist" which lends to their durability and color. Because the yarn is twisted so tight, the dye doesn't always infiltrate completely through, leaving the middle of the fabric white. This is how your True Religion jeans will have a nice well-worn color after you've worn and washed them a few times.